In the analysis of biological and chemical systems, a number of advantages are realized by the process of miniaturization. For example, by miniaturizing analytical and synthetic processes, one obtains advantages in: (1) reagent volumes, where reagents are rare and/or expensive to produce or purchase; (2) reaction times, where mixing or thermal modulation of reactants is a rate limiting parameter; and (3) integration, allowing one to combine multiple preparative and analytical/synthetic operations in a single bench-top unit.
Despite the advantages to be obtained through miniaturized laboratory systems, or microfluidic systems, early attempts at developing such systems suffered from a number of problems. Of particular note was the inability of early systems to control and direct fluid movement through microfluidic channels and chambers in order to mix, react and separate reaction components for analysis. Specifically, many of the early microfluidic systems utilized micromechanical fluid direction system, e.g., microfabricated pumps, valves and the like, which were expensive to fabricate and required complex control systems to be properly operated. Many of these systems also suffered from dead volumes associated with the mechanical elements, which prevented adequate fluid control substantially below the microliter or 100 nanoliter range. Pneumatic systems were also developed to move fluids through microfluidic channels, which systems were simpler to operate. Again, however, these systems lacked sufficient controllability to move small, precise amounts of fluids.
Pioneering developments in controlled electrokinetic material transport have subsequently allowed for the precise control and manipulation of extremely small amounts of fluids and other materials within interconnected channel structures, without the need for mechanical valves and pumps. See Published International Patent Application No. WO 96/04547, to Ramsey. In brief, by concomitantly controlling electric fields in a number of intersecting channels, one can dictate the direction of flow of materials and/or fluids at an unvalved intersection.
These advances in material transport and direction within microfluidic channel networks have provided the ability to perform large numbers of different types of operations within such networks. See, e.g., commonly owned Published International Application No. 98/00231 to Parce et al., and Published International Application No. 98/00705, describing the use of such systems in performing high-throughput screening operations.
Despite the wide-ranging utility and relative simplicity of these advances, in some cases, it may be desirable to provide simpler solutions to material transport needs within a microfluidic system. The present invention meets these and other needs.
In particular, the present invention provides material direction methods and systems that take advantage of certain flow properties of the materials, in conjunction with novel structures, to controllably direct material flow through an integrated microfluidic channel structure.
In a first aspect, this invention provides a microfluidic device for performing integrated reaction and separation operations. The device comprises a body structure having an integrated microscale channel network disposed therein. The reaction region within the integrated microscale channel network has a mixture of at least first and second reactants disposed in and flowing through the reaction region, wherein the mixture interacts to produce one or more products. The reaction region is configured to maintain contact between the first and second reactants flowing therethrough. The device also includes a separation region in the integrated channel network, where the separation region is in fluid communication with the reaction region and is configured to separate the first reactant from the one or more products flowing therethrough.
The invention also provides a device for performing integrated reaction and separation operations. The device comprises a planar substrate having a first channel disposed in the substrate containing at least first and second fluid regions. The first fluid region has an ionic concentration higher than an ionic concentration of the second fluid region, and the first and second fluid regions communicates at a first fluid interface. Second and third channels are disposed in the substrate, the second channel intersects and connects the first and third channels at intermediate points along a length of the first and third channels, respectively. The device also includes an electrokinetic material transport system for applying a voltage gradient along a length of the first channel, but not the second channel which electrokinetically moves the first fluid interface past the intermediate point of the first channel and forces at least a portion of the first fluid regions through the second channel into the third channel.
This invention also provides methods of performing integrated reaction and separation operations which include providing a microfluidic device comprising a body structure having a reaction channel and a separation channel disposed therein, the reaction channel and separation channel being in fluid communication. At least first and second reactants flow through the reaction channel in a first fluid region. The first and second reactants interact to form at least a first product within the first fluid region. The step of transporting through the first channel is carried out under conditions for maintaining the first and second reactants and products substantially within the first fluid region. At least a portion of the first fluid region is directed to the separation channel, which is configured to separate the product from at least one of the first and second reactants. The portion is then transported along the separation channel to separate the product from at least the first reactant.
The invention also provides methods of directing fluid transport in a microscale channel network comprising a microfluidic device having at least first and second intersecting channels disposed therein, the first channel being intersected by the second channel at an intermediate point. First and second fluid regions are introduced into the first channel, wherein the first and second fluid regions are in communication at a first fluid interface, and wherein the first fluid region has a higher conductivity than the second fluid region. An electric field is applied across a length of the first channel, but not across the second channel, to electroosmotically transport the first and second fluid regions through the first channel past the intermediate point, whereby a portion of the first fluid is forced into the second channel.
The invention also provides methods of transporting materials in an integrated microfluidic channel network comprising a first microscale channel that is intersected at an intermediate point by a second channel. First and second fluid regions are introduced serially into the first channel and are in communication at a first fluid interface. A motive force is applied to the first and second fluid regions to move the first and second fluid regions past the intermediate point. The first and second fluid regions have different flow rates or inherent velocities under said motive force. The different inherent velocities produce a pressure differential at the first interface that results in a portion of the first material being injected into the second channel.
The invention also provides methods of performing integrated reaction and separation operations in a microfluidic system, comprising a microfluidic device with a body, a reaction channel, and a separation channel disposed therein. The reaction channel is in fluid communication with the separation channel. At least first and second reactants are transported through the first region. The first and second reactants are maintained substantially together to allow reactants to interact to form at least a first product in the first mixture. The first mixture, including the product, is transported to the second region wherein the product is separated from at least one of the reactants.
The invention also provides methods of performing integrated reaction and separation operations in a microfluidic system, comprising a microfluidic device having at least first and second channel regions disposed therein, the first and second channel regions are connected by a first connecting channel. First reactants are introduced into the first channel region, the first reactants being contained within a first material region having a first ionic concentration. The first region is bounded by second regions having a second ionic concentration, the second ionic concentration is lower than the first ionic concentration. The first and second material regions are transported past an intersection of the first channel region and the first connecting channel, whereby at least a portion of the first material region is diverted through the connecting channel and into the second channel region.
In related aspects, the present invention also provides microfluidic devices for analyzing electrokinetic mobility shifts of analytes, where the device includes a body structure having a first microfluidic channel portion disposed therein, where the first channel portion has substantially no electrical field applied across its length. A second microfluidic channel portion is also included, but where the second channel portion has an electrical field applied across its length. The second channel portion being fluidly connected to the first channel portion. The device also includes a pressure source in communication with at least one of the first channel portion and the second channel portion for moving a material through the first channel portion into the second channel portion.
Relatedly, the present invention also provides methods of analyzing materials using the described devices. In particular, the methods of the invention analyze an effect of a first analyte on a second analyte. The methods steps include contacting the first analyte with the second analyte in a first microfluidic channel portion having substantially no electric field applied across its length. At least a portion of the first analyte and second analyte is transported to a second channel portion that is in fluid communication with the first channel portion and which has an electric field applied across its length. A change in the electrokinetic mobility of the second analyte, if any, is measured in the second channel portion, where a change in the electrokinetic mobility of the second analyte is indicative of an effect of the first analyte on the second analyte.
Similarly provided are methods of analyzing an electrokinetic mobility shift in a first analyte, which methods comprise flowing the first analyte through a first microscale channel portion having substantially no electrical field applied across it. The first analyte is then introduced into a second microfluidic channel portion. An electric field is then applied across a length of the second microfluidic channel portion but not across the length of the first a microfluidic channel portion. Finally, an electrokinetic mobility of the first analyte is measured under the electric field applied in the second channel portion.